The disclosure of Japanese Patent Application No. 2002-221651 filed on Jul. 30, 2002, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a vehicle steering apparatus with a lock mechanism.
2. Description of the Related Art
A vehicle steering apparatus with a lock mechanism is known, which includes a variable gear ratio mechanism that changes a turning amount of a turning wheel with respect to a steering amount of a steering wheel, and is provided on a steering shaft connected to a steering wheel; and a lock mechanism which restricts relative rotation of an input shaft and an output shaft of the variable gear ratio mechanism. An example of such a vehicle steering apparatus with a lock mechanism is disclosed in Japanese Patent Laid-Open Publication No. 2001-48032. The lock mechanism includes a lock holder which is provided on a rotor side of a motor mounted in the variable gear ratio mechanism; and a lock arm which is provided on a stator side of the motor. The lock mechanism is engaged by engaging the lock arm with a indented portion formed in a peripheral surface of the lock holder.
In this apparatus, if an opening width of the indented portion of the lock holder is small, there is a possibility that the lock mechanism cannot be engaged. For example, in the case where the lock mechanism is to be engaged when the motor is rotating, if the indented portion is not at a position at which the lock arm is engaged, the lock mechanism is not engaged appropriately.
In order to solve the problem, it is conceivable to make the opening width of the indented portion large. However, if the indented portion is made wide, there is large play between the lock arm and the lock holder when the lock mechanism is engaged. As a result, it is not possible to detect a positional relation between the lock holder and the lock arm accurately, and accordingly, it is not possible to control steering appropriately. For example, in the case where the lock mechanism is engaged while a vehicle is stopped, and then the lock mechanism is disengaged so as to start the vehicle, the rotational position of the rotating shaft of the motor at the time of vehicle start may be displaced from the rotational position thereof at the time of vehicle stop. In such a case, there is a possibility that the rotational position of the rotating shaft cannot be determined, which makes it difficult to control steering appropriately.
It is an object of the invention to provide a vehicle steering apparatus which can control steering appropriately.
A first aspect of the invention relates to a vehicle steering apparatus which includes a variable gear ratio device, a rotation detecting device, and a lock mechanism. The variable gear ratio device includes an input shaft connected to a steering wheel side and an output shaft connected to a turning wheel side, and changes a ratio between a steering angle input to the input shaft and a rotational angle output to the output shaft using rotation of a motor. The rotation detecting device repeatedly outputs, as the motor rotates, a series of a predetermined number of different signals, the signals differing according to the rotation of the motor, so as to detect a rotational position of a rotating shaft of the motor. The lock mechanism includes a lock holder which rotates together with the rotating shaft of the motor, and in which plural indented portions are formed at an outer periphery portion thereof, and an engagement member which is fitted on a stator side of the motor. The lock mechanism restricts relative rotation of the input shaft and the output shaft by inserting the engagement member in one of the indented portions. A play angle between the engagement member and the indented portion when the engagement member is inserted in the indented portion is smaller than a first rotational angle of the motor which is required for outputting all of the predetermined number of different signals.
According to the vehicle steering apparatus, the play angle when the lock mechanism is engaged by inserting the engagement member in the indented portion is smaller than the first rotational angle of the motor which is required for outputting all of the predetermined number of signals. Therefore, the rotation detecting device can be prevented from outputting the same signal at different rotational positions even if the motor rotates due to the play between the engagement member and the indented portion when the lock mechanism is engaged. Accordingly, the rotational position of the rotating shaft of the motor can be detected based on the output of the rotation detecting device, which makes it possible to control steering appropriately.